Carburetor



United States Patent Inventor Edward F. Fort Naperville, Illinois Appl. No. 722,524 Filed April 3, 1968 Continuation-impart of Ser. No. 565,910, July 18, 1966 Patented Sept. 22, 1970 Assignee Ethyl Corporation,

New York, N.Y., a corporation of Virginia CARBURETOR 13 Claims, 3 Drawing Figs.

1.1.5. Cl 123/119, 123/103, 123/108, 123/124 Int. Cl F02m l/10, F02d 11/08, F02m 23/04 Field of Search 261/52,

39,2;123/119F,119A,119,103,108,124A

[56] References Cited UNlTED STATES PATENTS 2,464,328 3/1949 Mallory 261/52X 2,694,559 11/1954 Gordon et al. 261/392 2,837,070 6/1958 Agar 261/392 2,982,275 5/1961 Doman et a1. 123/119 Primary Examiner-Wendell E. Burns Attorney-Donald L. Johnson ABSTRACT: Carburetor has choking connection arranged to apply partial choke at idle even when the engine is hot, to cause the carburetted fuel mixture to be richer at idle than at off-idle. Off-idle fuel mixture can be quite lean. Choke can be in a throat that has venturi-metered fuel supply elements providing all fuel for idle operation as well as fuel for off-idle operation. An additional throat can be used to supply richer mixture for maximum power operation.

/ Throttle Quiz/W11, Spring )M/vvv- 4 To Tlvvzfle I f'edai iatented Sept. 22, 1970 Sheet Patented Sept. 22 1970 Sheet mmw CARBURETOR The present application is a continuation-in-part of application Ser. No. 565,910 filed July 18, I966, but subsequently abandoned.

This invention relates to gasoline engine carburetors and more particularly to idle enrichment arrangements for such carburetors.

Among the objects of the present invention is the provision of a novel carburetor arrangement that gives a low exhaust emission.

In accordance with the present invention a carburetor is arranged to operate an internal combustion engine at off-idle conditions on a fuel mixture which is relatively lean so that the engines exhaust contains very little carbon monoxide and unburnt or partially burnt hydrocarbons. The carburetor also functions to supply a slightly richer fuel mixture at engine idling conditions which further reduces undesirableemissions during decelerations. It includes an induction passage having a choke valve mounted therein for movement between fully open and choking positions. One or more fuel jets can be downstream of the choke valve and can be connected to inject fuel into the induction passage during idle as well as off-idle engine operation, and form the combustion mixture for the engine.

The carburetor also includes a throttle valve within the induction passage downstream of the choke valve to regulate 'the supply of combustion mixture to the engine. Control elements are provided to operate the throttle valve and these elements are arranged to prevent the choke valve from opening beyond a predetermined choke position when the engine is idling. Such positioning of the choke valve during engine idle causes the carburetted fuel mixture to be slightly richer at idle than at off-idle engine operation. The overall effect of this arrangement is a significant reduction of exhaust emissions and engine operation with very good fuel economy.

The control elements may include a lever arm at least two inches long that magnifies the throttle movement and thus engages the choke valve mechanism only during the last five degrees or so of throttle closing. With such an arrangement the control elements have no effect on the enrichment when the throttle valve moves to off-idle positions, so that the choke valve can then move to the fully open position. The foregoing lever arm is also conveniently made adjustable as by bending to vary the enriching choke position of the choke valve at engine idle.

The carburetor arrangement of the instant invention may further include an automatic choking arrangement that urges the choke valve to choking positions when the engine temperature is below a predetermined minimum. A suction cylinder in the automatic choking arrangement is also provided to urge the choke valve open during heavily choked operation in response to suction downstream of the throttle valve in the induction passage.

The foregoing as well as additional novel features and advantages of the present invention will become apparent to one skilled in the art from the following description in conjunction with the accompanying drawings wherein similar reference characters refer to similar parts in which:

FIG. I is a partly broken away elevational view of a carburetor arrangement according to the present invention;

FIG. 2 is a view similar to FIG. 1 with the various components in a different operating position; and

FIG. 3 is an elevational view of a carburetor assembly pursuant to the present invention.

Referring in more particularity to the drawings, numeral represents a carburetor arrangement having at least one induction passage 12. A choke valve 14 movable between fully open and choking positions is suitably journaled in the induction passage by a pivot pin 16 extending through the side walls defining the passage. A hairspring 18 secured at its opposite ends to the carburetor housing and the choke connection, is provided to urge the valve to its fully open position. As shown, the choke valve can be unsymmetrically mounted so that air moving into the carburetor aids the spring 18 in urging the valve toward open position, as explained more fully below.

The carburetor 10 also includes a cam plate 20 secured to oneend of the pivot pin 16 by an out-of-round opening 22 in the plate that cooperates with a similarly shaped end portion on the pivot pin; A projection or stop 24 on the cam plate is positioned to cooperate with the throttle controls in a manner explained more fully below. The carburetor further includes a venturi 34 downstream of the choke valve 14, with a fuel jet 30 connected to a fuel bowl 32 and arranged to inject fuel into the induction passage at the venturi 34 during idle as well as off-idle engine operation.

A throttle valve 40 downstream of the fuel jet 30 is suitably journaled within the induction passage 12 by a pivot pin 42 ex tending through the side walls defining the passage. The throttle valve can include perforations 44 that provide the only passageways for the fuel mixture during engine idle operation. The perforate throttle valve can be replaced by an imperforate valve without departing from the scope of this invention, it being understood that if an imperforate valve is utilized it must be tilted slightly at idle to allow the fuel mixture to pass into the intake manifold. The throttle valve 40 is connected to a throttle pedal (not shown) by control elements including the linkage 46 so that the throttle valve opens to supply more fuel to the engine when the throttle pedal is depressed. A coil tension spring 48 or similar device can be provided to return the throttle valve to idling position when the throttle pedal is released.

The control elements include an actuating member 50 shown as a long lever arm connected to the throttle valve 40 at one end of the pivot pin 42. The actuating member has a terminal portion 52 that engages the projection 24 on the cam plate 20 when the throttle valve is in idling position. This engagement causes the cam plate 20 and the choke valve 14 to move in a clockwise direction, as viewed in FIG. 1, against the influence of spring 18 as the throttle valve moves to idling position. when the throttle valve reaches idling position the choke valve I4 is positioned in a predetermined choke position which increases the suction at the venturi 34 and causes mixture enrichment.

The control elements can be constructed so as to enable the predetermined choke position of the choke valve to be adjusted if desired. This may be accomplished by simply bending the actuating member 50 or by providing its terminal portion 52 with some other form of adjustment such as a threaded screw for example.

Carburetor 10 also includes an automatic choking arrangement which functions to urge the choke plate to its choking Y positionwhen the engine temperature is below a predetermined minimum such as 72F. The automatic choking arrangement includes a fast idle cam 62 having a series of steps 64, 66, 68, 70 that cooperate with a spur 72 secured to the actuating member 50. A longitudinally disposed slot 76in the fast idle cam enables the cam to move in a vertical direction I when the engine temperature is below the predetermined minimum. A pair of pins 78 secured to the side walls of the induction passage 12 extend through the slot 76 to limit and guide the vertical movement of the cam. 1 r

A bimetallic spring 80 constructed of two dissimilar metals having different coefficients of expansion is connected to urge' the cam plate 62 in the vertical direction when the engine temperature is below the minimum. Spring 80 urges its end portion 82 into engagement with an ear 84 secured to the fast idle cam 62.

The automatic choke also includes a rod 86 pivoted to the fast idle cam at 88 and connected to move the choke valve 14 to choking positions. The rod 86 has a terminal hook 90 that cooperates with an arcuate slot 92 in the cam plate 20. The arcuate slot is dimensioned to allow the choke valve 14 to move between the predetermined choke positon shown in' FIG. 1 and the fully open position shown in FIG. 2 without interference by the rod 86 when the throttle valve moves between idle and off-idle positions and the engine is warm.

The automatic choking'arrangement also includes an engine-operation-responsive means which may'take the form of a suction cylinder l00arranged to urge the choke valve 14- open during heavily choked operation. The suction cylinder has a suction chamber 102 connected through opening 103 to the induction passage downstream of the throttle valve. A flexible diaphragm 104 is responsive to the suction in the chamber 102 and this diaphragm moves to the right against the influence of a coil spring 106 in response to manifold vacuum in the suction chamber. A piston rod 108 having two portions pivotally connected together at 110 is arranged to move with the flexible diaphragm. The rod has a terminal hook 112 which slides in an arcuate opening 114 in a plate 1 16 secured to the pivot pin 16 of the choke valve connection. As clearly illustrated in the drawing, the plate 116 is secured to the pivot pin 16 at the end opposite that to which the cam plate 20 is secured. Plate 116 enables the suction cylinder 100 to move the choke valve 14 in the conventional manner toward its fully open position when the engine fires and its temperature is below the minimum.

In operation the various components of the present invention function to accurately supply a fuel mixture to an internal combustion engine under all operating conditions. The fuel is supplied by the fuel jet 30, although other or supplemental fuel supplies can be used. When the engine temperature is above that at which automatic choke spring 80 is actuated, the carburetor is in the condition illustrated in FIG. 1, and the idling mixture is enriched by the partial choke closing. The enriched mixture is preferably from about 14:1 to :1 in parts of air to fuel, by weight, although it can also be somewhat richer or leaner. In general the idle air-to-fuel mixture ratio is about one ratio number lower than the off-idle mixture ratio. For use in warmer climates or where the ambient temperatures do not fall below about freezing, the preferred idle mixture ratio can be slightly leaner, e.g. from 14.3: 1 to 15.5: 1.

When the engine is operating at off-idle conditions the throttle valve is in an open position as shown in FIG. 2, and the terminal portion 52 of the actuating member 50 is positioned away from the projection 24 on the cam plate 20. The actuating member remains in the foregoing position until the throttle pedal is released and the throttle return spring takes over to urge the throttle valve 40 back toward its idle position. As the throttle valve moves toward idling position the terminal portion 52 of the actuating member engages the projection 24 on the cam plate 20. Continued movement of the actuating member causes the cam plate to rotate in a clockwise direction as viewed in FIGS. 1 and 2 of the drawing. The cam plate continues to rotate until the throttle valve reaches idling position and this occurs when the peripheral portion of that valve engages the side walls defining the induction passage. The above sequence of operation positions the choke valve 14 in its predetermined choke position for idle enrichment, and the valve remains so positioned until the throttle pedal is again depressed. When the throttle valve opens, the actuating member moves away from the choke valve, leaving it free to return to its fully open position.

With the choke valve in the position shown in FIG. 1, the suction developed at the venturi 34 is somewhat greater than the suction produced when the choke valve is fully open, and the greater suction sucks more fuel into the induction passage. This helps an engine to idle smoothly, and also keeps the mixture burning better during engine deceleration, so that less unburnt and partially burnt fuel is passed out the engine's exhaust. The fact that the enrichment is accompanied by some choking is particularly beneficial inasmuch as the choking helps to mix the fuel better with the air so that the different cylinders of an engine receive more uniform mixtures. By providing a slightly richer mixture at engine idling conditions the fuel supply at off-idle operation can be leaner, and the leaner mixture at off-idle burns cleaner and with less undesirable exhaust emissions than is possible when the idle mixture is used for power generation.

The arcuate slot 92 in the cam plate 20 does not retard the choking effect of the choke spring 80 inasmuch as the upper smallest degree of thermally-induced choking will lift the fast idle cam 62 and cause its fast idle step 66 to prevent closing of the throttle to its normal or so-called hot idle position. In other words, thermal choking is effected with the carburetor off idle and with rod 86 always in engagement with the top of slot 92.

Slot 114 has its lowest portion a little longer than otherwise needed in order to maintain idle enrichment notwithstanding the actuation of suction cylinder 100 by the intake manifold suction developed at idle. The suction cylinder will accordingly not try to open the choke valve any further than to the idle enrichment position. This type of action does not significantly affect the automatic choke operation inasmuch as the most significant aspect of the choking insofar as the suction cylinder is concerned is the heavier end of the choking. The heavy choking is what is needed to start a very cold engine and yet must be quickly lightened when the engine begins to fire uniformly. If desired, however, the suction cylinder 100 can be connected to unwind the inner end of choke spring instead of as shown in FIG. 1.

The carburetor of FIG. 1 does not need more than about 10 of choking to effect all the idle enrichment that can be used. One reason for this is that the carburetor has a venturi that meters all idle fuel as well as off-idle fuel. This venturi is relatively small in cross-sectional area, about 0.09 to about 0.18 square inches at its narrowest portion, for every cubic inches of total piston displacement in the engine that uses the carburetor. Such a fuel supply system is simpler to manufacture and maintain but only has a limited range of mixture supply rate. It is accordingly advisable to use this combination as the primary or low power carburetion in a system that also has a secondary carburetor that delivers a mixture for high power operation. Such an arrangement is shown in FIG. 3.

Some carburetors can have air horns substantially wider than indicated by the proportion of air horn width to venturi diameter in the drawings. As the air horn width increases with respect to venturi diameter, the degree of choking needed to effect the idle enrichment of the present invention also increases, and can reach 30 in extreme cases. There are situations, as for example where the fuel jet air bleed vents above the choke blade, where the choke blade may have to be tilted as much as 50 to get the desired enrichment.

For the idle enrichment of the present invention the fuel supply in the carburetor bowl or the like should not be subjected to pressure variations that correspond to the choke-induced changes in carburetor throat pressure. Such variations in fuel pressure will tend to keep the fuel flow from increasing in response to the choking. Thus if a carburetor bowl is used it should not be vented to the carburetor throat at a location below the choke.

With the choke type idle enrichment of the present invention the range of operation for the primary or low power carburetor is increased because the choking extends the venturis functioning to somewhat smaller mixture speeds. The primary venturi can accordingly be somewhat larger than without the enrichment, and the second carburetor can be arranged to come into operation at somewhat higher speeds than otherwise needed. The relatively rich mixtures supplied by the secondary carburetors can then be limited to the highest power outputs, thus providing greater fuel economy. This is particularly significant when the engine supplied by the carburetor operates with high air flow rates at idle, as for example by having its idle ignition timing set relatively more delayed than the usual 6 to 10 before top center.

By tapering the fast-idle steps of cam 62, as indicated at step 66, the cam will be more readily permitted to drop down when choke spring 80 unwinds, even though the throttle is kept closed. When so closed spur 72 engages whichever step is at the appropiate level, and continuing to run the engine with step 66 so engaged will warm up the engine and spring 80 to the point that the choking becomes excessive until cam 62 drops. The inclined nature of step 66 keeps the engaging contact force of spur 72 from seriously delaying the dropping of the cam. In fact the illustrated inclination can even caus the spur contacting force to provide a small component that facilitates the dropping of the cam.

Alternatively the choke can be permitted to open in the foregoing situation without having the cam drop, as by having choke spring 80 act directly against choke plate rather than the cam 62. Choke plate 20, after it is lifted (along with cam 62) into choking position by spring 80, will then be lowered as that spring warms up without requiring the lowering of cam 62. Slot 92 permits this opening movement of the choke, so that no other change is needed.

When the carburetor has an idle fuel supply port not operated by a venturi, the degree of choking needed to effect idle enrichment is substantially higher than discussed above. A choke plate may have to be moved to almost completely full choke in such a modification to obtain the desired idle enrichment, inasmuch as choking systems do not fully close off all air supply. in either type of modification, however, the idle enrichment should terminate when the throttle is about 5 from idle position.

Additionally, since the choke valve of the present invention moves toward open position in fixed relationship to the throttle opening, there is no sudden leaning of the fuel mixture as the throttle valve is opened, thus preventing stalls and surging. Yet because of the relative position of the various components the fuel mixture is not over-rich at low speed cruise conditions.

While the above described embodiment constitutes the preferred mode of practicing this invention, other embodiments and equivalents may be resorted to within the scope of the invention which is claimed as follows.

I claim: 4

l. A carburetor having an induction passage, a choke valve within the passage mounted for movement between fully open and choking positions, mechanical bias structure connected to the choke valve and biasing it toward the open position, a throttle valve within the induction passage downstream of the choke valve, the control elements connected to operate the throttle valve, the control elements being further connected to prevent the choke valve from opening beyond a predetermined choke position when the throttle valve is in idling position, to cause the carburetted fuel mixture during hot operation to be richer at idle than at off-idle.

2. The carburetor of claim 1 in which the induction passage has venturi-metered fuel supply elements that provide all fuel for idle as well as fuel for off-idle engine operation.

3. The carburetor of claini l in which the control elements are connected to disengage from the choke valve when the throttle valve moves to off-idle positions so that the choke valve can then move to fully open position.

4. The carburetor of claim 3 in which the control elements include a lever arm at least two inches long that acts to restrain the choke valve in accordance with a magnified aspect of the throttle valve movement.

5. The carburetor of claim 1 including an automatic chok ing arrangement connected to urge the choke valve to choking position when the engine temperature is below a predetermined minimum.

6. The carburetor of claim 5 in which the automatic choking arrangement includes an engine-operation-responsive means connected to urge the choke valve open during heavily choked operation.

7. The carburetor of claim 6 in which the engine-operationresponsive means includes a suction cylinder that urges the choke valve toward open position in response to suction downstream of the throttle valve in the induction passage.

8. The carburetor of claim 1 in which the induction passage is connected to deliver during hot operation a combustion mixture having an air-fuel ratio of at least as high as 14.5:1 at off-idle.

9. A carburetor having an induction passage, a choke valve within the passage mounted for movement between fully open and choking positions, a throttle valve within the induction passage downstream of the choke valve, throttle actuating elements connected to operate the throttle valve and further connected to hold the choke valve in partially closed mixture-enriching position whenever the throttle valve is in idling position, the throttle actuating elements being otherwise disengaged from the choke valve, to cause the carburetted fuel mixture during hot operation to be richer at idle than at off-idle.

10. The carburetor of claim 9 in which there is a fuel bowl connected to supply the fuel, and the fuel bowl is vented to a location not subject to choke-induced pressure variations.

11. The carburetor of claim 9 in which there is a second induction passage paralleling the first and connected to supply fuel mixture for high power operation, and the first induction passage has venturi-metered fuel supply elements that provide all fuel for idle as well as fuel for off-idle engine operation.

12. The carburetor of claim 11 in which the control elements are connected to establish an idle operation at an air flow rate corresponding to that required for idling with the ignition timing more delayed than 6 before top center.

13. The carburetor of claim 2 in which the throttle valve has a multiplicity of spaced perforations that provide essentially the only passageways for the fuel mixture during idling. 

